Unwarping an almost-mosaic of sword

[Mark Stoutjesdijk]

Hi,

I photographed a Japanese sword (naginata, actually), and managed to get VERY decent stitching. Unfortunately, even with a lens focal distance override of 4000mm, I still get a significant warp in the resulting image. See the attached small JPG.

There is a ruler in the image, and "all" I think I need to do is straighten that. Messing around with photo tools like Affinity took a lot of time and ended with disappointing results.

I'm hoping someone can point me in the right direction to fix this. It would be ideal if I would only need to adjust a setting in PTGUI. But any other tool that I could use to straighten the ruler in the bottom of the panorama would be great as well.

Best, Mark

[PTGui Support]

Hi Mark,

Mosaics can be tricky to stitch, they only work if the subject is
completely flat. Any depth will cause parallax. Parallax generally will
cause unfixable stitching errors and it will also cause the optimizer to
overcompensate by adjusting parameters in an unwanted way, which is
what's happening here.

Ideally all control points should be placed in a flat plane,
perpendicular to the camera. You could try placing all control points on
the background surface only. This would lead to misalignments on the
sword's surface but perhaps they are not noticable.

Another thing you could try is to force the optimizer to use the same
roll angle for all images. Switch to Advanced mode, go to the Optimizer tab:
- switch to Advanced optimizer
- Optimize globally: only Fov,a,b,c. Disable shift
- For all images except the middle one: optimize only yaw and pitch, not
roll. For the middle image optimize nothing.
- Go to Lens Settings and press the Reset Button next to Lens Correction
- Go to Image Parameters and set all Roll angles to zero
- Then run the Optimizer (press F5)

I assume this will lead to a straight image, but there will be stitching
errors. It's a trade off.

Kind regards,

Joost Nieuwenhuijse
www.ptgui.com

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[John Houghton]

Mark, I tried using Photoshop's Transform tools on your image, but correcting the irregular distortions is very difficult and the result (attached) is not really adequate.

John